1. Field of Invention
The present invention relates to a semiconductor device, and more particularly to an electrostatic discharge (ESD) protection structure.
2. Description of Related Art
ESD is a phenomenon in which charges are accumulated on a non-conductor or a non-grounded conductor and then suddenly transfer and discharge through a discharge path. The circuits in ICs can be damaged by ESD. For example, a charge carrying object, such as a human body, a machine for packaging ICs or an apparatus for testing ICs, can discharge to an IC chip when the charge carrying object is in contact with the IC chip. Thus, the IC chip is damaged or broken by the transient power of ESD.
Usually the ESD tolerance for commercially available ICs is required to pass the human body mode (HBM) test at 2 kV and the machine model (MM) test at 200 V. In order to sustain the above-mentioned high-voltage ESD tests, the large-sized ESD protection device for ICs is usually applied. This large-sized device is designed as a multi-finger shape in the layout to save the chip area as much as possible. Although the multi-finger protection device can save the chip area, such layout usually causes the non-uniform turn-on issue of the device.